Laser polishing of vidicon's glass substrates

Abstract

URGENCY OF THE OBJECT AND INNOVATIVE APPROACHMany micro-and nanoelectronic, micro-and nanooptic devices include different films and layers deposited at the surfaces of dielectric substrates. Properties of these films and layers sufficiently depend on properties of the substrate surface. Therefore substrate surface preparation before layers and films deposition is very important. One of the main parameters of the surface is its roughness that influence on such parameters of thin layers as specific resistance, electric strength, chemical resistance etc. By mechanical treatment of the surface its roughness is defined by the size of polishing powder grain. That is why preparation of the surface with low roughness is laborious one. Besides, preliminary mechanical grinding with coarse-grained powder causes appearance of near-by-surface cracked layer, which can be removed by deep mechanical, chemical or flame polishing. Laser polishing is sort of last one. The problem of laser polishing was repeatedly discussed 1, 2 . 10.6 μm СО 2 -laser is the only acceptable one, as all glasses well absorb radiation at this wave length. The regime of continuous radiation is used in most cases, for which typical duration of influence by surface scanning is several milliseconds. Though the beneficial effect was obtained (in before mentioned and other papers), the technique is not wide spread. In our opinion the reason of this is that there are problems connected with phenomena specific for laser polishing: hydrodynamical waves in the softening layer and thermomechanical tensions in the substrate. Both of them are aggravated by the three-dimensional locality of laser action. This situation can be changed by using of short nanosecond laser pulses -in this case the heated layer of substrate decreases and the problem becomes not so critical.For instance, receiving plate of vidicon is the glass substrate with conductive, photosensitive and high-resistance layers deposited on it. Thickness of CdSe photosensitive layer with impurities is 0.4-0.6 μm, working voltage supplied to the target is 10 -25 V, in these conditions electric intensity can reach 20 kV/mm in the CdSe layer. Such heavy processing environment of vidicon target requires high-level homogeneity of photosensitive and conductive layers and high quality of the glass substrate surface at which the layers are being deposited.Defects and imperfections of the work surface of glass substrate cause appearance of large size defects in In 2 O 3 conductive layer deposited at it. Those defects become crystallization centers in CdSe layer. Insufficient electric strength of crystallized regions result in appearance of electrical escape in them and breakdown of the photosensitive layer by working voltage supply to the pickup plate. As a result those defect regions become insensitive to luminous flux and blank spots arise at the vidicon target. Number of reject targets can reach tens of percent.For yeild increasing it is necessary to improve quality of the glass substrates surface. We tried to so...